[PATCH v2 2/2] KVM: Fetch guest cr3 from hardware on demand

[Avi Kivity <avi@redhat.com>]

Instead of syncing the guest cr3 every exit, which is expensince on vmx
with ept enabled, sync it only on demand.

Signed-off-by: Avi Kivity <avi@redhat.com>
---
 arch/x86/include/asm/kvm_host.h |    2 ++
 arch/x86/kvm/kvm_cache_regs.h   |    2 ++
 arch/x86/kvm/svm.c              |    5 +++++
 arch/x86/kvm/vmx.c              |   23 +++++++++++++++++------
 4 files changed, 26 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 4461429..07a20f4 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -117,6 +117,7 @@ enum kvm_reg {
 
 enum kvm_reg_ex {
 	VCPU_EXREG_PDPTR = NR_VCPU_REGS,
+	VCPU_EXREG_CR3,
 };
 
 enum {
@@ -533,6 +534,7 @@ struct kvm_x86_ops {
 			    struct kvm_segment *var, int seg);
 	void (*get_cs_db_l_bits)(struct kvm_vcpu *vcpu, int *db, int *l);
 	void (*decache_cr0_guest_bits)(struct kvm_vcpu *vcpu);
+	void (*decache_cr3)(struct kvm_vcpu *vcpu);
 	void (*decache_cr4_guest_bits)(struct kvm_vcpu *vcpu);
 	void (*set_cr0)(struct kvm_vcpu *vcpu, unsigned long cr0);
 	void (*set_cr3)(struct kvm_vcpu *vcpu, unsigned long cr3);
diff --git a/arch/x86/kvm/kvm_cache_regs.h b/arch/x86/kvm/kvm_cache_regs.h
index a6bf8db..3377d53 100644
--- a/arch/x86/kvm/kvm_cache_regs.h
+++ b/arch/x86/kvm/kvm_cache_regs.h
@@ -75,6 +75,8 @@ static inline ulong kvm_read_cr4_bits(struct kvm_vcpu *vcpu, ulong mask)
 
 static inline ulong kvm_read_cr3(struct kvm_vcpu *vcpu)
 {
+	if (!test_bit(VCPU_EXREG_CR3, (ulong *)&vcpu->arch.regs_avail))
+		kvm_x86_ops->decache_cr3(vcpu);
 	return vcpu->arch.cr3;
 }
 
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 5d0f945..78d13de 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1323,6 +1323,10 @@ static void svm_decache_cr0_guest_bits(struct kvm_vcpu *vcpu)
 {
 }
 
+static void svm_decache_cr3(struct kvm_vcpu *vcpu)
+{
+}
+
 static void svm_decache_cr4_guest_bits(struct kvm_vcpu *vcpu)
 {
 }
@@ -3765,6 +3769,7 @@ static struct kvm_x86_ops svm_x86_ops = {
 	.get_cpl = svm_get_cpl,
 	.get_cs_db_l_bits = kvm_get_cs_db_l_bits,
 	.decache_cr0_guest_bits = svm_decache_cr0_guest_bits,
+	.decache_cr3 = svm_decache_cr3,
 	.decache_cr4_guest_bits = svm_decache_cr4_guest_bits,
 	.set_cr0 = svm_set_cr0,
 	.set_cr3 = svm_set_cr3,
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index fb09685..2ae25e5 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -180,6 +180,7 @@ static int init_rmode(struct kvm *kvm);
 static u64 construct_eptp(unsigned long root_hpa);
 static void kvm_cpu_vmxon(u64 addr);
 static void kvm_cpu_vmxoff(void);
+static void vmx_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3);
 
 static DEFINE_PER_CPU(struct vmcs *, vmxarea);
 static DEFINE_PER_CPU(struct vmcs *, current_vmcs);
@@ -1836,6 +1837,14 @@ static void vmx_decache_cr0_guest_bits(struct kvm_vcpu *vcpu)
 	vcpu->arch.cr0 |= vmcs_readl(GUEST_CR0) & cr0_guest_owned_bits;
 }
 
+static void vmx_decache_cr3(struct kvm_vcpu *vcpu)
+{
+	/* Can only be called with EPT enabled */
+	if (enable_ept && is_paging(vcpu))
+		vcpu->arch.cr3 = vmcs_readl(GUEST_CR3);
+	__set_bit(VCPU_EXREG_CR3, (ulong *)&vcpu->arch.regs_avail);
+}
+
 static void vmx_decache_cr4_guest_bits(struct kvm_vcpu *vcpu)
 {
 	ulong cr4_guest_owned_bits = vcpu->arch.cr4_guest_owned_bits;
@@ -1879,6 +1888,8 @@ static void ept_update_paging_mode_cr0(unsigned long *hw_cr0,
 					unsigned long cr0,
 					struct kvm_vcpu *vcpu)
 {
+	ulong cr3;
+
 	if (!(cr0 & X86_CR0_PG)) {
 		/* From paging/starting to nonpaging */
 		vmcs_write32(CPU_BASED_VM_EXEC_CONTROL,
@@ -1893,8 +1904,11 @@ static void ept_update_paging_mode_cr0(unsigned long *hw_cr0,
 			     vmcs_read32(CPU_BASED_VM_EXEC_CONTROL) &
 			     ~(CPU_BASED_CR3_LOAD_EXITING |
 			       CPU_BASED_CR3_STORE_EXITING));
+		/* Must fetch cr3 before updating cr0 */
+		cr3 = kvm_read_cr3(vcpu);
 		vcpu->arch.cr0 = cr0;
 		vmx_set_cr4(vcpu, kvm_read_cr4(vcpu));
+		vmx_set_cr3(vcpu, cr3);
 	}
 
 	if (!(cr0 & X86_CR0_WP))
@@ -3734,11 +3748,6 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu)
 	if (vmx->emulation_required && emulate_invalid_guest_state)
 		return handle_invalid_guest_state(vcpu);
 
-	/* Access CR3 don't cause VMExit in paging mode, so we need
-	 * to sync with guest real CR3. */
-	if (enable_ept && is_paging(vcpu))
-		vcpu->arch.cr3 = vmcs_readl(GUEST_CR3);
-
 	if (exit_reason & VMX_EXIT_REASONS_FAILED_VMENTRY) {
 		vcpu->run->exit_reason = KVM_EXIT_FAIL_ENTRY;
 		vcpu->run->fail_entry.hardware_entry_failure_reason
@@ -4055,7 +4064,8 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu)
 	      );
 
 	vcpu->arch.regs_avail = ~((1 << VCPU_REGS_RIP) | (1 << VCPU_REGS_RSP)
-				  | (1 << VCPU_EXREG_PDPTR));
+				  | (1 << VCPU_EXREG_PDPTR)
+				  | (1 << VCPU_EXREG_CR3));
 	vcpu->arch.regs_dirty = 0;
 
 	vmx->idt_vectoring_info = vmcs_read32(IDT_VECTORING_INFO_FIELD);
@@ -4322,6 +4332,7 @@ static struct kvm_x86_ops vmx_x86_ops = {
 	.get_cpl = vmx_get_cpl,
 	.get_cs_db_l_bits = vmx_get_cs_db_l_bits,
 	.decache_cr0_guest_bits = vmx_decache_cr0_guest_bits,
+	.decache_cr3 = vmx_decache_cr3,
 	.decache_cr4_guest_bits = vmx_decache_cr4_guest_bits,
 	.set_cr0 = vmx_set_cr0,
 	.set_cr3 = vmx_set_cr3,
-- 
1.7.1